NVD / CVE Program· CNA Linux

CVE-2024-56581: btrfs: ref-verify: fix use-after-free after invalid ref action

Noroxi assessment

Priority: Monitor (action score 31/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.23% (FIRST EPSS).
Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
Fixed version: Linux Linux 4275ac2741941c9c7c2293619fdbacb9f70ba85b, 6370db28af9a8ae3bbdfe97f8a48f8f995e144cf, 6fd018aa168e472ce35be32296d109db6adb87ea; azl3 kernel 6.6.57.1-7 on Azure Linux 3.0 6.6.64.2-1; azl3 kernel 6.6.64.2-1 on Azure Linux 3.0 6.6.64.2-1.

Low priority for now. Upgrade to Linux Linux 4275ac2741941c9c7c2293619fdbacb9f70ba85b, 6370db28af9a8ae3bbdfe97f8a48f8f995e144cf, 6fd018aa168e472ce35be32296d109db6adb87ea; azl3 kernel 6.6.57.1-7 on Azure Linux 3.0 6.6.64.2-1; azl3 kernel 6.6.64.2-1 on Azure Linux 3.0 6.6.64.2-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: btrfs: ref-verify: fix use-after-free after invalid ref action At btrfs_ref_tree_mod() after we successfully inserted the new ref entry (local variable 'ref') into the respective block entry's rbtree (local variable 'be'), if we find an unexpected action of BTRFS_DROP_DELAYED_REF, we error out and free the ref entry without removing it from the block entry's rbtree. Then in the error path of btrfs_ref_tree_mod() we call btrfs_free_ref_cache(), which iterates over all block entries and then calls free_block_entry() for each one, and there we will trigger a use-after-free when we are called against the block entry to which we added the freed ref entry to its rbtree, since the rbtree still points to the block entry, as we didn't remove it from the rbtree before freeing it in the error path at btrfs_ref_tree_mod(). Fix this by removing the new ref entry from the rbtree before freeing it. Syzbot report this with the following stack traces: BTRFS error (device loop0 state EA): Ref action 2, root 5, ref_root 0, parent 8564736, owner 0, offset 0, num_refs 18446744073709551615 __btrfs_mod_ref+0x7dd/0xac0 fs/btrfs/extent-tree.c:2523 update_ref_for_cow+0x9cd/0x11f0 fs/btrfs/ctree.c:512 btrfs_force_cow_block+0x9f6/0x1da0 fs/btrfs/ctree.c:594 btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754 btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116 btrfs_insert_empty_items+0x9c/0x1a0 fs/btrfs/ctree.c:4314 btrfs_insert_empty_item fs/btrfs/ctree.h:669 [inline] btrfs_insert_orphan_item+0x1f1/0x320 fs/btrfs/orphan.c:23 btrfs_orphan_add+0x6d/0x1a0 fs/btrfs/inode.c:3482 btrfs_unlink+0x267/0x350 fs/btrfs/inode.c:4293 vfs_unlink+0x365/0x650 fs/namei.c:4469 do_unlinkat+0x4ae/0x830 fs/namei.c:4533 __do_sys_unlinkat fs/namei.c:4576 [inline] __se_sys_unlinkat fs/namei.c:4569 [inline] __x64_sys_unlinkat+0xcc/0xf0 fs/namei.c:4569 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f BTRFS error (device loop0 state EA): Ref action 1, root 5, ref_root 5, parent 0, owner 260, offset 0, num_refs 1 __btrfs_mod_ref+0x76b/0xac0 fs/btrfs/extent-tree.c:2521 update_ref_for_cow+0x96a/0x11f0 btrfs_force_cow_block+0x9f6/0x1da0 fs/btrfs/ctree.c:594 btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754 btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116 btrfs_lookup_inode+0xdc/0x480 fs/btrfs/inode-item.c:411 __btrfs_update_delayed_inode+0x1e7/0xb90 fs/btrfs/delayed-inode.c:1030 btrfs_update_delayed_inode fs/btrfs/delayed-inode.c:1114 [inline] __btrfs_commit_inode_delayed_items+0x2318/0x24a0 fs/btrfs/delayed-inode.c:1137 __btrfs_run_delayed_items+0x213/0x490 fs/btrfs/delayed-inode.c:1171 btrfs_commit_transaction+0x8a8/0x3740 fs/btrfs/transaction.c:2313 prepare_to_relocate+0x3c4/0x4c0 fs/btrfs/relocation.c:3586 relocate_block_group+0x16c/0xd40 fs/btrfs/relocation.c:3611 btrfs_relocate_block_group+0x77d/0xd90 fs/btrfs/relocation.c:4081 btrfs_relocate_chunk+0x12c/0x3b0 fs/btrfs/volumes.c:3377 __btrfs_balance+0x1b0f/0x26b0 fs/btrfs/volumes.c:4161 btrfs_balance+0xbdc/0x10c0 fs/btrfs/volumes.c:4538 BTRFS error (device loop0 state EA): Ref action 2, root 5, ref_root 0, parent 8564736, owner 0, offset 0, num_refs 18446744073709551615 __btrfs_mod_ref+0x7dd/0xac0 fs/btrfs/extent-tree.c:2523 update_ref_for_cow+0x9cd/0x11f0 fs/btrfs/ctree.c:512 btrfs_force_cow_block+0x9f6/0x1da0 fs/btrfs/ctree.c:594 btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754 btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116 btrfs_lookup_inode+0xdc/0x480 fs/btrfs/inode-item.c:411 __btrfs_update_delayed_inode+0x1e7/0xb90 fs/btrfs/delayed-inode.c:1030 btrfs_update_delayed_i ---truncated---

HighCVSS 7.8 · v3.1—No exploit Fix available

Memory safety

BDU:2025-03594

Published: Dec 27, 2024
Updated: Aug 5, 2026
EPSS: 0.2% · 14th percentile
CWE: CWE-416

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 31 / 40 · 7.8 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 7.8
CNA · Linux: 7.0; 0.8 point gap

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
linux	linux kernel	cpe:2.3:o:linux:linux_kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

linux linux kernel4.15 and later · before 5.4.287
linux linux kernel5.5 and later · before 5.10.231
linux linux kernel5.11 and later · before 5.15.174
linux linux kernel5.16 and later · before 6.1.120
linux linux kernel6.2 and later · before 6.6.64
linux linux kernel6.7 and later · before 6.12.4
linux linux kernel6.13

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

Linux Linux
- 4.15affected
- fd708b81d972a0714b02a60eb4792fdbf15868c4 and later · before dfb9fe7de61f34cc241ab3900bdde93341096e0eaffected · git
- fd708b81d972a0714b02a60eb4792fdbf15868c4 and later · before 6fd018aa168e472ce35be32296d109db6adb87eaaffected · git
- fd708b81d972a0714b02a60eb4792fdbf15868c4 and later · before d2b85ce0561fde894e28fa01bd5d32820d585006affected · git
- fd708b81d972a0714b02a60eb4792fdbf15868c4 and later · before 6370db28af9a8ae3bbdfe97f8a48f8f995e144cfaffected · git
- fd708b81d972a0714b02a60eb4792fdbf15868c4 and later · before 4275ac2741941c9c7c2293619fdbacb9f70ba85baffected · git
- fd708b81d972a0714b02a60eb4792fdbf15868c4 and later · before a6f9e7a0bf1185c9070c0de03bb85eafb9abd650affected · git
- fd708b81d972a0714b02a60eb4792fdbf15868c4 and later · before 7c4e39f9d2af4abaf82ca0e315d1fd340456620faffected · git
- before 4.15not affected · semver
- 5.4.287 and later · up to and including 5.4.*not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	linux	before 6.1.123-1	6.1.123-1
Debian:13	linux	before 6.12.5-1	6.12.5-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
90Now
CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
89Now
CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
85Now

Published before and after this one in the same product

← EarlierCVE-2024-56579Dec 27, 2024 · media: amphion: Set video drvdata before register video device
22Monitor
← EarlierCVE-2024-56580Dec 27, 2024 · media: qcom: camss: fix error path on configuration of power domains
22Monitor
Later →CVE-2024-56582Dec 27, 2024 · btrfs: fix use-after-free in btrfs_encoded_read_endio()
31Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Linux Linux	4275ac2741941c9c7c2293619fdbacb9f70ba85b	Vendor (CNA)
Linux Linux	6370db28af9a8ae3bbdfe97f8a48f8f995e144cf	Vendor (CNA)
Linux Linux	6fd018aa168e472ce35be32296d109db6adb87ea	Vendor (CNA)
Linux Linux	7c4e39f9d2af4abaf82ca0e315d1fd340456620f	Vendor (CNA)
Linux Linux	a6f9e7a0bf1185c9070c0de03bb85eafb9abd650	Vendor (CNA)
Linux Linux	d2b85ce0561fde894e28fa01bd5d32820d585006	Vendor (CNA)
Linux Linux	dfb9fe7de61f34cc241ab3900bdde93341096e0e	Vendor (CNA)
azl3 kernel 6.6.57.1-7 on Azure Linux 3.0	6.6.64.2-1 · CBL-Mariner Releases	Microsoft (MSRC)
azl3 kernel 6.6.64.2-1 on Azure Linux 3.0	6.6.64.2-1 · CBL-Mariner Releases	Microsoft (MSRC)
cbl2 kernel 5.15.173.1-2 on CBL Mariner 2.0	5.15.176.3-1 · CBL-Mariner Releases	Microsoft (MSRC)
cbl2 kernel 5.15.173.1-2 on CBL-Mariner 2.0	5.15.176.3-1 · CBL-Mariner Releases	Microsoft (MSRC)
cbl2 kernel 5.15.176.3-1 on CBL Mariner 2.0	5.15.176.3-1 · CBL-Mariner Releases	Microsoft (MSRC)
debian:linux	6.1.123-1 · Debian:12	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Someone with local access to the system can trigger it.
A low-privileged account is enough.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Local
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-primary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

Fix✗ → ✓Sep 28, 2026, 10:09 PM UTC

For records you follow, these changes also arrive as notifications. →

References

git.kernel.org/stable/c/4275ac2741941c9c7c2293619fdbacb9f70ba85b

Show all references (8 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records